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Brent, Nautilus has no drop weights. I know of no modern navy submarines ( excluding deeb sea vessels like Alvin ) that has. In emergencies we blow our tanks with HP air - either LP air or - if to deeb for that directly 200 bar air. The latter is a 75000 liter bank, with very dry air. There are different schools of thought in this field - Carsten e.g. has no windows and drop weights, while I have designed with big windows ( yet very thick ones ) and no drop weight. One reason for this is that Nautilus is designed for much shallower depth than CSSX, and at shalow water windows are less dangerous than at deep - and that at deep water a drop weight may be more efficient than blowing tanks. Carsten has put great effort into complex stress calculation and non destrutive testing - his boat is designed to collapse at greater than 500 meters - and will be used to 250 and tested to 320...as I remember. Nautilus - in a simple calculation - can take 400 plus, but without NDT and with her large windows I don´t expect to go any deeper than 100. Most Scuba diver can tell you that the fun is at less than 30, where sunlight and vegitation exist. It is quite posible we will never pass 50 and still be absolutely happy with the boat. The more precise you know the properties of the pressure hull the closer to the edge you can safely go - reflected in the differences Nautilus / CSSX. Back to the subject... One of the negative sides to experience is that you may become overzealous - and after some 1200 times of floding tanks and controling boyancy - I feel I got it rigth - only this time I was tricked by the open flange. All in all the experience has made me more kean to get the final jobs done and begin diving. Carsten has a point about closed hatches - and belive me we were ready had it ever looked critical. When looking back at a situation - its sometimes importent not just to be satisfied with the fact that it ended good and never really was dangerous. The problem here was that it was luck, not planing or knowlidge that saved the day. Fact: I failed. I could have sunk the whole thing sending four quite capeble trained men and one older person in the water - I can´t promis everyone would have made it. That is sometimes part of being Captain - that responsebility. I will do my best to learn. Whitout my imgination this would look like a small inconvinience...but thats me...thinking what could have happened. Like they say at half machine - its the small accidents that prevents the big ones... Best regards, Peter From: brenthartwig@hotmail.com To: personal_submersibles@psubs.org Subject: RE: [PSUBS-MAILIST] A voyage on Nautilus, and the story of the boyancy crisis...and how we almost lost control... Date: Mon, 25 Aug 2008 13:43:59 -0700 Greetings Peter, Thank you for sharing that information and showing use your humility. It makes you a better person in my view and we can all learn from the experience. I've been reading Carsten's Euronaut building updates of late, and he's always piping in and connecting some different system. Slowly but surely he will be ready. But he will likely feel very ready as well. I think at times I'm doing pretty well and that I'm pretty smart, but then I trip over my shoe laces or do some other absent minded thing. Then I think to myself, you think your going to build and use a submarine and survive the experience. Do you have drop weights on the Nautilus? I've always wondered why large military subs don't have drop weight systems. Perhaps someone here will enlighten me? I would expect it has some thing to do with them wanting to be able to submerge again to get away from surface dangers. Does the Euronaut have drop weights Carsten? I would think when venting any tanks for the first time, it should be done in very shallow water, or have the sub attached to a crane. It seems to me that Kraka needs a longer operational life. Why put her in a museum so soon? Regards, Brent Hartwig From: uc3nautilus@hotmail.com To: personal_submersibles@psubs.org Subject: [PSUBS-MAILIST] A voyage on Nautilus, and the story of the boyancy crisis...and how we almost lost control... Date: Mon, 25 Aug 2008 21:32:39 +0200 Dear Psubbers, One of the things that are quite seldom here is operational stories - what you experience when going out with your subs. Half an hour ago Nautilus arrived at her base with me a serious lesson richer - and here is the story...of the boyancy crisis and how we almost lost control... Todays voyage was to start at 1400 hours, with the crew arriving at 1300. We intended to take a joy ride through the Copenhagen Harbor, and into the sound - ending at our northern base. Its about 8 nautical miles and we expected to sail for about two hours. We had a very special crew, and a very special guest - Richard. R. is a "very high ranking" retired US navy submariner - who at age 70 visited the Nautilus. He has had the command of several US diesel and nuclear submarines. Also we had Daniel, a former Danish navy submarine TKO - technical officer and one navy surface ship navigator. Ad two navy seals - off duty - and you have a crew with quite some experience. Nautilus performed very well, and as we passed the shipyard area where she was build, we came ashore and visited the drydock where Kraka lies. She is operational, but disused and awaits going to the Danish Technical Museum. All the crew were most happy, in no small part Richard. The new coffee machine in the gally was tested and worked well. Into the sound we increased speed to flank. We had three person in the sail, no fuel in the tanks ( we run her from a jerrycan ) and all tanks blown. As a result the stability margin is marginal - al as expected. We had som osciliations giving some 30 deg. swings as we whent flank speed, som we discussed ways to increase stabilty. One of the questions to be asked is if the free uncontroled water surface in the main tanks will make the boat more unstable than the potential stabilicing effect of the boat deaper in the water. To test this we came to stop, and manually wented air from the fwd and rear main ballast tanks. The boat is not finished. There are no blowing tubes or valves inside, but form outside - via a hose you can blow the tanks. Also the diving valves at this stage can only be operated from outside. The fwd. valve was opened, and this tank floded about 50 %. The rear tank was opened, and it floded about 50 %. Nautilus was lying at a deep trim - her fwd hatch closed, and with a free board of about 2 meters to the sail hatch. Aparently stable... Then one of the deck crew reports - "Sir, - we are still sinking in the stern" And yes - the rear diveplane was now slowly submerging...ok - I go check the valve, its closed and tight...but we are still sinking slowly...water begins covering the rear deck... I gues I build submarines in part to feal that thrill...Ups...did we mis a step here ?...like mission control in Houston you start to figure out - what in the hell is going on - while staying calm. You try to be in advance of the situation - How deep will we except this to go - what actions need to be taken - how much boyancy do we have in the sail - what is the mechanisem behind this... Then mr. Madsen, Master and Comander of his home made submarine flotilla - realises that the rear trim tank - enourmours at some 1.5 m3, is floding uncontroled due to a flange remowed ( to mount the new tube. ) Frankly - at this point I did not know when this was going to be stable. We could have ended up much like the U-505 ( se pic from her US navy capture ) with only the top of the sail and the bow above water. If so, I would have ordered the sail hatch closed - engine shut down and the crew out of the engineroom and on deck. Likely our fwd hatch would never have gone under since most of the bouyancy in the bow was still there. At the end - with both hatches closed the boat would stay surfaced a some angle, but holy shit, how stupid can a man be ? As it was Nautilus stabiliced with the water just below the deck level, and with the bow at about normal trim. No problem at all, Kraka has lived her life like that - but this was not because of my talent or smartness, no - just simple luck. Carsten and his Germans will now tell me how stupid I am - and I agree. I for my part told Richard the story of the Seydlitz, a German WWI battlecruiser returning to port after the Battle of Jutland with all of the fore deck under water...only to be repaired and returned to service...and scuttled at Scarpa. The good thing about it was that everybody was calm and working together to finde the cause - and we quickly did - and then we continued at slow first. Indeed with her tanks part floded Nautilus was far more stable, and we increased to flank speed while seeing the bow raising under the hydrodynamic force of the rear planes. ( so are we going to sink when we slow down ?! ) We did not - we got fine to port, blew the tanks, and there she is safe and sound. Richard, our navy comander - gave me a US Navy officers badge, and said a lot of nice things - that I really fell I don´t deserve after this ordeal that was all my fault - but I have decided to learn from it. Not so much in the detail - since its a specialty - that we will never see again, but as a lesson in the safe operation of big dangerous machines. I may sound stupid, but whenever you get to the edge of what you have done before, slow down, analyse carefully before taking the next sted. I failed to do so - because of the exelent way the boat and crew was performing in other irralevant ways. The missing part for that flange cost about 2 US doller. Have a nice day - and don´t play with water with out adult attention... Best regards, Peter Hold dig opdateret på dagens Gossip. Få messenger på mobilen. Få 30 nye Superheroes smileys. Hent dem Gratis her. |